Isomerization of olefins



May 5, 1942- R. F. RUTHRUFF ISOMERIZATION OF OLEFINS Filed Sept. 5, 1940 v'UNITED STATES' PATENT FFICE rsom'aar'za'rloN-or oLEFxNs naher-c F. autumn, chicago'. m. application september 5, 1940, serial No. 355,501 4 1s claims. (cl. 26o-esa) "This invention relates to the catalytic conversion rof parafllnic and. olennic hydrocarbons containing 'four carbon atoms to the molecule into liquid hydrocarbons of high octane number boiling' within the usual motor fuel range. vMore particularly, this inventionv relates to the catalytic conversion of paramnic and oleilnic hyart. In a morev restricted sense, this invention relatesto Athe catalytic conversion of less reactive olefins containing four carbon atoms to the molecule into other oleilns of thefsame molecularv weight but greater reactivity. Specically, in its more restricted sense, this invention relates to the catalytic conversion of butene-l into butene- 2 and to-the catalytic conversion of butene-2 into isobutene.

Briefly, one embodiment of my invention eml l braces the catalytic dehydrogenation of par--` aillnic hydrocarbons `'containing vfour carbon atoms to the molecule,.subjecting the'resulting products -to 'catalytic isomerization whereby the less reactive olefl'ns therein are converted to more reactive oleiins, subjecting the resulting products to catalytic polymerization whereby' oleflns are converted to liquids and hydrogenating the resulting liquids to produce a material of highroctane number.

It, is aprincipal object of this invention to provide a catalytic unitary combination process for thel conversion o f paraflinc and oleilnichy-` drocarbons containing four carbon atoms to ythe molecule into ajhigh yield oi high1 octane number liquid hydrocarbons boiling within the usual motor fuel range. In a 'more restrictedsenae, it is aprincipal object 'of this invention to provide a catalytic process for the conversion of less reactive olefins containing fourl carbon atoms to the molecule intoother olefins ofthe same molecular weight but of greater reactivity. Specifically, in amore restrictedsense, it is a principal object'pf this invention to provide a catalytic process forthe conversion of butene-l into butene-2- and for 'the `catalytic conversion of butene-2 into isobutene. Other objects of this of the drawing, fresh charge to the unit, comprising paramnic hydrocarbons containing four atoms of carbon to the molecule and representing, for example, a fraction of the proper boiling range fobtained from natural gas, is introduced through line I.- The fresh-charge may be Preheated if desired, for example, by being brought into indirect Iheat exchange relationship with a hot stream from a source hereinafter to be diescribed in `exchanger 2, the thus preheated charge then passing throughline 3 to coll I disposed in furnace setting 5. The charge, during passage through coil l is brought to the proper reaction temperature and is then discharged,

, via line` C, to reactor] containing a suitable minor proportion of an oxide of an element of -the left hand subgroups of groups IV.- V and VI- within limits, more or less interchangeable. In'

other words, within limits. similar o r even identical results are obtained by exposing the charge at a relatively high temperature for a relatively short time or by exposing the charge for a relatively lon`g time at a relatively low temperature. In general, when employingsome of the more active dehydrogenation catalysts, for example,

activated alumina plus 4 to 8% chromium oxide. temperatures of from about 500 to 650 C. may

be employed with space velocities of about 200to imrentionwill become apparent as the descrlption thereof proceeds.

For the more complete understanding of my invention, reference may be had to the drawing 7500. Satisfactory results are obtained when opera`ting at 600- C. and a space velocity ofv 2500. Preferably, moderate to low pressures are employed, 'for example, 50 pounds per square inch gage or less.

-While a single catalytic dehydrogenation re-v actor is shown, it is to be understood that all catalysts employed gradually lose activity when on stream and accordingly require periodic regeneration'. Accordingly, for continuous operation, provisin must 'be .made for the regeneration ofv one part 'of the total catalyst while another portionJ is dehydrogenating the charge. 'I'his may be accomplished, for example, by using a pair of reactors, each similar to 1, the catalyst in one being regenerated by burning accumulated car.

`bonaceous deposits therefrom by a stream of air or dilute air while the catalyst in the other is simultaneously exercising its dehydrogenating action on lthe charge, the functions of the two reactors being reversed periodically. Also, for this type of operation, the' moving catalysttechnique-is especially suitable or the suspended catalyst technique may be employed. For a more complete exposition of the various methods of employing catalysts mentioned briefly in the infor example, by having the lcatalyst heated by hot combustion gases surrounding the tubes, said heated gases being obtained during the regeneration of another portion of the catalyst.

=Reacton products from dehydrogenation ,re-

' actor 'I leave by line 8 and are partially cooled in indirect heat exchanger 2 with fresh charge.

If desired, but not necessarily, hydrogen may nowl be removed from the reaction products. However, leaving hydrogen in the reaction products' until after the olen isomerization reaction to follow results in certain advantages as will 'hereinafter become apparent. If the hydrogen is not removed from the catalytic dehydrogenation y reaction products, hydrocarbons containing four carbonatoms to the molecule yand obtained, ior

example, from the, gases produced during cracking and/or reforming operations may be introduced viav line 9. As will hereinafter become apparent, the refinery gas cut may form thesole fresh feed to the process, rio natural gas butanes being introduced through -line I.

The resulting 'gasstrearm consisting essentially of hydrogen and hydrocarbons containing four carbon atoms to the molecule is further cooled as necessary by. passage through cooler Il following which it passes through line I I to isomerization reactor I2 which containsa suitable isomerization catalyst. Certain metal pyrophosphates, particularly stabilized metalfpyropho'sphates, for example, pyrophosphates of copper, mercury;l zinc, magnesium, cobalt, iron or aluminum especially when in a stabilized form areemployed for 4the purpose. I have found that copper pyrophcsphate, especially stabilized copper pyrophosphate, to be particularly eiiicacious. Specific examples of the preparation` of such catalysts will be given hereinafter.

' Reaction conditions to lbe maintained in isomerization reactor `I2 depend to a large extent upon the exact catalyst employed. However, as a guide, when using stabilized copper pyrophosphate-prepared in accordance with Example 1,

below, a low to moderate superatmospheric pressure, preferably in the neighborhoodv of 100 pounds per square inch or less is used at a tem; perature in the approximate range 250450 C., the time of contact being in the neighborhood of 5 to 100seconds more or less Particularly good results are obtained when operating at 2 5 pounds per square inch, a temperature of 325- C. and a contact time of seconds.

It '1s obvious that the above outlined conditions during isomerization it is highly` desirable to avoid polymerization as muchas possible. To

this end,the operating pressure during isomerization should be as low as feasible.v Also, pref- 5 erably, the charge to the isomerization reactor is diluted withv aninert. gas, -steam for example, to

Acut down the olefin concentration and accordingly' The reaction productsleaving isomeiization ref i5 actor I2 through line I3 consist essentially of hy 'drogen, butanes that escaped catalytic dehydrol genation and the two olenes, butene-2 and isobutene. Under proper catalytic isomerization' conditions as outlined-above the butene-l con- 20 tent ofthe gas stream is practically nil and the c isobutene-butene'2 ratio is unity or more.

Hydrogen is now removed from the gas stream. Any suitable means may be employed for the purpose, for example, absorption. To this end, the reaction products are cooled in cooler Il,

are compressed toa moderate superatmospheric pressure, 'for example,.50 to 300 pounds per square inch depending'upon the temperature o'f the cool'- ing water and other considerations, in compressor I5, the resulting material being sent to separator I5. Uncondensed components of \the reaction products are sent by `valved line I1 to absorber I8-- Absorber IB is` provided with means for facilitating liquid-vapor contact thereirr such as bubble trays I9 although other suitable devices for the purpose, for example, Raschig ringpacking or Berl saddles may be used i-f desired. Cold absorber oilis introduced into absorber I8 by line 20'and is contacted with the ascending gas stream in said absorber. Unabsorbedgas, consisting essentially of hydrogen, is discharged through valved line 2|` while rich absorber oil leaves through line 22, is moved by pump 23 through indirect heat exchanger 24 where it is heated by a hot stream from a source hereinafter to be described, following which it enters stripper 25. Stripper 25 is preferably provided with means for facilitating liquid-vapor contact, top cooling means and bottom. heating means. vMeans for 50 facilitating liquid-vapor contact may .take the form of bubble trays 25, althoughl other suitable means, such as Raschig ring packing or Berl saddl'e's may be employed. For bottom heating, liquid may be removed from trapv out tray 21 positioned 55 .near the bottom of stripper 25, moved by pump l 28 through suitable heater 29 and thence by line ployed, either alone or in combination with the device described or other devices, for example, an

tower or a similarly positioned closed coil through whichl heated uid maybe circulated.

removed through line 3l', cooledin cooler 32 and discharged into separator 33. -Any uncondensed 'material may be removedcontinuousl'y or intermittently at frequent lntervalsthrough valved e line 3 4 while liquids may be moved bypump 35,

vide reflux therein. Other suitable cooling means may be employed, either alone or in combination with the device described or other devices, for exare within the catalytic polymerization range and ample, an upper positioned closedcoil through or other similar'. inert gases open steam coil positioned near the bottoziof the For top e cooling, gaseous products from stripper 25 may berr a portion of-these being passed via valved line I5 back to the upper portion of stripper 25to pro- .which com uuid is circuiad, or cela uuidv or suitable propertiesfrom an outside'sou'rce may be added to the upper portion o f stripper 25 to provide open reflux therein;

Abwrbed materials are removed from rich e absorber oil in stripper' 25.' Stripped absorber oil leaves by line Il, is moved by pump 3l through'.

exchanger 24 wherein it is partially cooled by rich absorber oil, thence through cooler 38 and iinally back to absorber I8 via line 28. Absorbed .ma

. teriais eliminated in stripper' 25leave through line-ll. @The recirculation'oi part of these back tothe stripper to provide openrefluxtherein has already been described. Liquid material not used -to provide reflux passes through valved'line 48 and joins with liquids from separator I5 which leave this element through valved line 4|. The resulting composite stream may be processed without further rectificationif desired by passing it through valved linev 42, the valves kin valved linesfand 48 being closed. Preferably however the small amount of components boiling lower than hydrocarbons having four carbons in the molecule and small am'o'unts of polymers formed during isomerization are removed by fractionation in tower 45.- In such a case the composite feed stream is sent to tower 45 throughyalvedline 48; valved line 48 also being open while valved line 42 is closed. Tower 45 is' provided with means for facilitating liquid-vapor contact, bottom heating means and upper disposed cooling means as described connection with stripper 25. Light components yoriginally presentin the composite feedstream are removed through valved line 45 and are preferably sent to absorber I8 via line 41. By operating in this way gas consisting essentially of hydrogen is eliminated throught 'valved line 2l while gases consisting essentially of hydrocarbons of less than four carbon atoms to .the molecule' are eliminated through valved line 34. Material f consisting essentially of hy'- drocarbons containing four carbon atoms to the molecule are removed through valved line 48. 'Ihe small amount of polymers formed during .isomerization are removed through valved line 44.

Hydrocarbons containing four carbon Yatoms'to the molecule which are removed through valved line 48 from tower 45 are preferably compressed .to a high superatmospheric pressure by pump 48 .and are passed through coil 50 in furnace setting 5I wherein the materials are heated to the desired catalytic polymerization reaction temperature.

The thus heated polymerization charge passes through line 52 to catalytic polymerization 'reac-z tsr 53. A wide variety of catalysts may be employed .in polymerization reactor 53. Among these may be mentioned clays, especially acid activated clays, vsodium aluminum chloride, lithium aluminum chloride, alumina hydfolytically absorbed on' silica gel, synthetic silica-alumina complexes, calcined phosphoric acid-lrieselguhr mixtures, phosphoric acid on charcoal, phosphoric acid on silica and the like. Especially good results are obtained using certain metal pyrophosphates, specifically, pyrophosphates of copper, mercury, zinc, magnesium, cobalt, iron or aluminum, partcularly such metal pyropho'sphates in the unstabilized lor even promoted condition. Speciiic examples of the preparation of such catalysts will hereinafter appear, The exact operating conditions to be employed depend to a great extent upon the exact composition of the gas being treated, the catalyst selected and many other factors. `As an example of suitable operating conditions when using unstabilized copper pyrorated naphtha of high octane rating. To accom? passed over this contact agent at a temperature of 160 to1 180- C., a pressure of 1500 pounds per square inch and a rate of 40 'cubic feet of charge measured as a gas at standard conditions per hour per pound of eataiyst.- Under these operating conditions olefin polymerization was praccooling means .within reaction vessel v53.' This 'cooling may be accomplished, for example, by

bypassing a portion of the feed to furnace coil 50 aroundsaid'coil by a line (not shown) and introducing said cold feed into reactor 53 at one or more points: I As usual, the polymerization catalyst ysooner or'later becomes more or less inactive and must .then be replaced or regenerated. When copper pyrophosphate is employed, while itr can be regenerated, the active life of the catalyst is so long that, when exhausted, it can be replaced rather than being regenerated without sacrice in economic advantage. catalyst is regenerated or replaced it is advisable to use a plurality of reactors so that operations' are continuous. It is common practice to employ three or more reactors, the catalyst in one being regenerated or replaced whilethe remaining ones are on stream. Flow in the on stream reactors is commonly countercurrent,A that is, fresh feed is contacted withthe most nearlyexhausted catalyst. When two or more reactors are employed on stream simultaneously 'itis commonpractice to install intercoolers between successive reactors to remove part or-ali of the heat generated yby the polymerization reaction.

Products from catalytic reactor -53 leave through line 54, the' products` may be cooled in exchanger 55 prior to passage to` separator 55.

`.out tray 58 by means of`pump 6|` while'gas, con-fv sisting essentially of the butanes passes through valved line 82 back tothe catalytic` dehydrogenation zone. Liquid polymers of higher boiling range than desired may be discharged from tower 51 by valved line 88., It will be noted that the small quantity of 'polymers formed during isomeriation and removed from tower 45 by valved line 44 are also'charged to tower 51 for fractionation..

The liquid polymer discharged through/line 68 from `tower 51 is hydrogenated by suitable well known methods and means to produce a satuby pump 83 and is mixed with polyniei'ofthe de-` K-sired boiling range from pump 8|, the resulting composite feed passingby line 84 to coil 65 in furnace setting 66. On passage througircoil 55 the'mixture is brought to reaction temperature and is discharged via transfer line ilto hydro# genation reactor 88. A number of contact agents may be employed ijn reactor 88 but most of these Whether the l .4 y v l may be roughly divided into two groups"`(al nickel, especially nickel on a suitable support and (b) oxides and/or sulfldes.. of sixth group metals, for example, molybdenum and tungsten, particularly such compounds on suitable supports. The exactreaction conditions to be employed in reactor 68 depend largely on the type of catalyst employed. catalysts of type (u) operate under comparatively mild conditions but are prone to become poisoned. vcatalysts of type (b) are less active but are extremely stable. With type (o) catalysts pressures of from 500 to 3000 pounds per square inch mayjbe employed at 260 to 370 C.

With type (a) catalysts pressure may be 50 to 500 pounds per square inchat a temperature of say 150 to 300 C.l With both types of catalysts it is preferable to use a large excess of hydrogen, for example, 5 or more moles of hydrogen per mole of polymer charged to the reactor.

'The choice of catalyst to be employed 1in the hydrogenation zone is largelygoverned by the sulfur content of the feed thereto. When a sulfur free feed or a feed of low sulfur content is 'elnployed, vit ispreferable to employ the more active type catalyst. The sulfur content of the feed to catalysts may be used. lWith high sulfur feeds.

the isomerization catalysts and polymerization catalysts usually become exhausted more rapidly thanwhenv sulfur free or low vsulfur-.charging stocks .are employed. The regeneration of the polymerization `catalyst vhas already been d'e scribed. The isomerization catalyst zone'may be arranged similarly for similar ends. Provision' shouldlikewise preferably be made to allow regeneration of the active type of'hydrogenation catalyst, and still maintain continuity of operation, The life of the-less activetypeof hydrogenation catalyst is so long usually that -provi' sions for regeneration while-maintaining conti-v 'nuity ofoperation are usually unnecessary. When ,such catalysts, 'after use. for weeks or months, nnally become exhausted the whole unit can be .shut down and the catalyst replaced. Obviously, if desired, the charge to the dehydrogenation zone may be caustic washed or otherwise treated to remove rsulfur and the same may be done prior to any or any combination of the succeeding catalytic zones.

Reaction products from Vhydroge'nation` reactor l by-methods well known to those skilled in the art fresh feed to the system may consist of eithernatural gas butanes or the C4 cut from refinery gas. With either charging stock or with a mix` ture of the two, the hydrocarbon gases are largely converted into liquid hydrocarbons of high octane number, l

4The advantages that follow allowing the hydrogen produced during catalytic dehydrogenation to remain in the gas streamuntil after the olens have been catalytically isomerizedhave already been mentioned. It should -be understood'however that, if desired, the hydrogen may .be removed immediately afterthe catalytic dehydrogenation step. This is easily accomplished by passing (after cooling) the gas mixture produced in catalytic dehydrogenation reactor l to separator I6, the light'gas eliminated therefrom going to absorber I8. This Vgas is treated in 4a manner identical with that previously described and the hydrogen free gas consisting essentially of hydrocarbons of four carbon atoms to the' molecule are' eliminated from. stripper 25 via valved line 4|. This mixture, after preliminary stabilization is desired in a tower similar to l5, is then passed through a heater and thence to isomerizer I2. lsomerized products then pass to poiymerizer 53 and the remaining course is identical to that already described. As will be apparentto those'skilled in the art, by a simple group of manifolds (not shown) the unit of the drawing can be made to operate with hydrogen removalafter isomerization and prior to polymerization (as shown) or after dehydrogenation and prior to isomerization not shown).

It will be evident that by practicingthe process just described a. higher yield of higher octane number liquid hydrocarbons is obtained than has j number about as high as that from straight isobutene, for example, 92 to 96. However, if more than one molecule of butene-2 reacts per molecule of isobutene reacting or if appreciable amounts of butene-l react, the resulting polymer, after hydrogenation is of comparatively low octane number.- 'I'he lisobutane--butane ratio in most natural gases is very low, averaging vsay 0.25. Accordingly, on catalytic dehydrogena` tion of such a mixture, the isobutene normal butenes ratio in the' products is also low, again Abeing in the neighborhood of 0.25. Also, the isobutene-normal butenes ratio in cracking or red8 leave through line 69, are cooled in exchanger 10 andv after partial or complete pressure reduction across valve 'Il are discharged into separator 12; l Excess hydrogen 'is eliminated through' valved line 13 and issent back tol valved line 2| forming unit gases is low, averaging perhaps 0.35. Obviously, if` dehydrogenated natural gas or cracking or reforming unit gases or mixtures thereof is subjected to catalytic polymerization, ii

polymeriztatlon is complete or nearly so the.

polymer product, after hydrogenation, will have a-very low antiknock value. If, on the other for recycling. If desired, part or all of this stream 't may be introduced into absorber I8 by suitable Ameans (not shown). Hydrogenated high octane ultimate product is eliminated through valved line 1I, 4This material may be further processed ifJ desired, for example, by fractionation in `a suitable tower (not shown).'

genation, will have a high octane nuinber but the yield oi such a product will be low.

lIi; is evident that if necessary the exclusive '75 .By the practice of the present invention,

assises prior to polymerizatiomcomplete olefin cleanup during polymerizationresults in the production of a polymer which, after hydrogenation, has a high octane number.` During the isomerization reaction, all or practically all'of the butene-l forms butene-2 while a large proportion ofbutene-2 is converted to isobutene. With the isobutene originally present in the charge to the lsomerizer, plus that resulting from isomerization it is easily possible to obtaina product exhibiting an isobutene-butene-2 ratio of one 0r more. When such a mixture is catalytically polymerized, complete or practically complete` olefln'cleanup may be obtained with the production lof aproduct which, after hydrogenation, hasa high octane number.

Suitable catalysts for use in the dehydrogenation reactor and the hydrogenation reactor have already been described briefly and 'methods for the preparation o1' these are well known to those skilled in the art. The preferred isomerization and polymerization catalysts are less familiar and accordingly 4their preparation will be described.

'I'he pyrophosphate catalysts employed in the practice of the instant invention may be pre- -pared by any appropriate method. All of them may be made by metathesis, for example, -by the addition of a solution of-a soluble pyrophosphate, for example, sodium pyrophosphate, toa solution of a salt of the metal in question, the precip` itated metal pyrophosphate being removed'from the mother liquor by vfiltration or otherwise iolliquor by filtration or otherwise following which the compound is washed and ignited to form the desired pyrophosphate in conformity withthe following reactions: 2MHPO4=M2P2O1+-H2O and 2Nz(llPO4)3== N4(PzO1)s-i3HO. Or, if desired, as a modificationl of the method just described, certain of thepyrophosphates exhibiting catalytic activity may lbe prepared by first forming the metal monoammonium orthophosphate of the general formula MNH4PO4 (where M represents 1 a dlvalent metallfremoving a metal monoammonium orthophosphate from the mother liquor der'. are dried to form the nnai cataiyst. n

desired. prior to extrusion, about 33% of finely divided carbon based on the final dried catalyst may be added. This materlalaids in binding the catalyst particles together and has other benecial eil'ects.

The catalyst formed in. accordance vlan Example 1 is eminently suitable for use in the catalytic isomerization of olefins as previously v described. By. some mechanism, as yet imper- Exactly similar to Example except that instead of using 10% excess of sodium pyrophosphate, an amount about 5% less than thaty stoichiometrically equivalent to the copper sulfate is employed. The catalyst ofthis exa'mple is eminently suitable for use in the catalytic polya merization of oleflns as previously described.

Such 'a catalyst, made without an excessl of" sodium pyrophosphate is unstabiliz'ed. If desired, an even more active catalyst may be prepared by incorporating promoters, such as iinelyA divided metals, especially finely divided metals in the activated state, in the catalyst. For example, from 0.5 to 5% z inc dust (based on the copper employed) may' be suspended in the sodium pyrophosphate solution used in theA preparation of the catalyst -or the zinc dust may be 'suspended in the coppersalt'solution or it may by filtration or` otherwise, washing following which the compound is ignited to formthe desired pyrophosphate in accordance with the following equation: 2MNH4PO4=M2P2O1+2NHJ +1120.

For the better understanding of methods that may be employedl to form the pyrophosphate catalysts of the instant invention a fewv specific examples of a few suitable procedures. will be given. f f

Example 1 A 0.2 molar solution of sodium pyrophosphate is added to a 0.2 molar solutionbof a copper salt such as copper sulfate, the sodium pyrophosphatev vbe distributed between the two.

. Example 3 A dilute solution df magnesium sulfate is made decidedly acid with hydrochloricacid, using about 2 to 3 cc."concentrated acid per gram of magnesium salt. Following this about 5 g. diammonium hydrogen phosphate is addedper gram of magnesium salt and there is then added slowly, with stirring, 5% ammonia solution until the reaction mixture is distinctly alkaline. The resulting reaction mixture is allowed t stand several hours (with stirring if desired) following which the magnesium ammonium orthophosphate is removed by filtration, washed with 5% A dilute solution of zincsulfate is carefully neutralized using methyl red (or orange) indicator. The resulting solution is brought tothe boil, is agitated and treated with a large excess of a 15% solution of diammonium hydrogen orthophosphate. After addition is complete the solution is kept hot for an hour and is then allowed to cool following which the precipitate is removed by filtration, is. washed with cold water and ignited to give zinc pyrophosphate.l Cobalt pyrophosphate can be made in an analogous manner. BothA of these catalysts vare most y suitablev for use in olefin isomerization but may be used Ain olefin polymerization if desired;I

While my invention has been described with respect to certain specific embodiments thereof it is to be understood that other-modes of applying the principles of the invention may be enh, ployedin lieu of those explained and accordingly the specic embodiments presented are not intended to limit-.my invention except'l insofar as these may be set forth inthe follow' Lclaim: v

1. -In a process for the conversion of a. hydrocarbon fraction comprising straight chain bu- .ig claims.

tenes. the step including contacting said hydrocarbon fraction with a pyrophosphateoffa metal selected from the group consstingfof copper, mercury', zinc, iron, aluminum, cobalt and mag- Vnesium at a temperature of from`ab`out'250 C. to

450 C. lfor a time period and under .apressure such that isomerization of said straight chain butenes to isobutene proceeds at asubstantially higher rate than butene polymerization.

2. In a process for the conversion of a hydrocarbon fraction comprising straight chain butenes, the lstep including contacting said hydrocarbon fraction 'wana stabilized 'pyrophosphate of a metal selected from the group consisting of y copper, mercury, zinc, iron', aluminum, cobalt and magnesium at a temperature of from about 250.

C. to 450v C. for a time period and under a pressure such that isomerization of said straight chain butenes to isobutene proceeds at a substantially higher rate than butene polymerization.

3. In a process for the conversion of a hydrocarbon ,fractioncomprising straight chain bul tenes,y the step including contacting said hydrocarbon fraction with mercury pyrophosphate atv a temperature of from about 250 C. to 450 C. for a time period Aand under a pressure such that isomerization o! said straight chain butenes to. isobutene proceeds at a substantially higher rate than butene polymerization.

V4. In a process for the conversion of a hydrocarbon fraction comprising straight chain bu- Itenes, the stepincluding'contacting said hydrocarbon fraction with stabilizedfmercury pyrophosphate at a temperature of from aboutf250 C. to 450 C. for a time periodand under a pres-- sure such that isomerization of said straight chain butenes'to isobutene proceeds'at a substantially higher rate than butene polymerization.

` \5. In a process for the conversion ofa hydrocarbon'fraction comprising straight chain butenes; the step including contacting said hydrocarbon fractionwith zinc pyrophosphate at a temperature of from about 250 C. to 450"C.. for

a time period and under a pressure such that isomerization -ofv said straight chainv butenes to isobuteneproceeds at a substantially higher rate than butene polymerization: g v Y l 6.. In a process for the conversion of a hydrocarbon fraction comprising straight chain butenes, the step including'contacfng said hydrocarbon fr'action` witl i` stabilized 'zinc pyrophosphate at a temperature of from about 250 C.v to` 450 C. for a timevp'eriod and under a pressure suchl that isomerization di.' `said straight chain butenes to isobutene proceeds .at a substantially higher rate than butene polymerization.

' 7. In aprocess for the yconversion ofa hydrocarbon fraction comprising straight chain buftenes,the. step including contacting said hydrocarbon fractioniwith copper pyrophosphate at a temperature of from about 250 C. to 450 C. for

a time period and under a pressure such that isomerization .of straight chain buten'esl to isobutene proceeds. at a vsubstantially higher rate than bute`ne polymerization.

8. In a process `for the conversion of a hydrocarbon fraction comprising straight chain butenes, the step including contacting said h'ydrocarbon fraction with stabilized copper' pyrophosphate ata temperature of from about 250 C. to

4450 Cffor a time period and under a pressure such that isomerization of said straight chain butenes to isobutene proceeds at a substantially higher rate than butene polymerization.

9. vIn-the process for the conversion of a normal butene to isobutene, the step including contacting said normal vbutene with a pyrophosphate of a metal s elected"from the group consisting of copper, mercury, zinc, iron, aluminum, cobalt and magnesium at a temperaturey of from about 250 C. to 450 C.-for a time period and under a pressure such that isomerization of the normal bul normal butene proceeds at a substantially higher rate thanbutene polymerization.

butene to isobutene, the step including contacting said normal butene with mercury pyrophosphate at a temperature of from about 250v C. to 450 C. for a time period and under a pressure such that isomerization ofnormal butene proceeds at a substantially higher rate than butene polymerization.

12. In a process'ior the conversion of a normal butene to isobutene, the step including contact- 85 ing said normal butene with stabilized mercury pyrophosphate ata' temperature of from about 250 C. to 450 C. for a time period and under a pressure such that isomerization of the normal butene proceeds at a substantially higher rate v40 than butene polymerization.

13. In a process forthe conversion of a normal butene to' isobutene, the step including contacting said normal butene with zinc pyrophosphate at a temperature from about' 250 C.. to 450 C. for a time period and under a pressure such that isomerization of the normal butene proceeds at a -substantially0 higher; rate than butene poly-- merization.

14. In a process for the conversion of a normal butene to isobutene, the step including contacting said'normal butene with stabilized zinc pyrophosphate at atemperature of from about 2509., C. to 450`C. for a-time period and under a pres- 15. In a process for theconversion of a normal butene to isobutene, the step including contacting said normal butene with'copper pyrophosphate at a temperature of from about 250 C. to 450 C.

isomerization of the normal 'butene proceeds at a substantially higher 'ratei` than butene poly- ROBERT F. RUTHR'UFF.

11. In a process for the conversion of a normal for a time period and under a pressure such that. 

